This simple module adds a few additional mail icons to the chatter. There are extra colors that amplify a certain status: if the email was sent, bounced, not sent (server error etc.) or planned. There's also an additional toolbar on icon hover, so the small pop-up window that shows up when you put a cursor on the icon, containing more specific information of the email, like who's the recipient or what went wrong when sending an email if it failed.

Also, this module allows you to set up a note about newly created meetings, which will automatically show up in the chatter, however this requires code adjustments, see the link on the right how to do it.